Recalibrating the speedometers

[TH]

I will be putting on either 285x75R16 or 255x85R16 tires on my 2500HD Duramax. My dealership advises me that the largest size tire that their computer can recalibrate to is the 265x75R16. This tire is still about 1.5" smaller in diameter than the ones I intend to use.

I suspect that there might be aftermarket fixes for this...anyone know of where or who offers this? I'd like to ensure I get the right speedometer readings etc.

Will tranny shifts be affected by larger diameter tires?

[afp]

When I had my truck reflashed for the 265s I originally ran, it only corrected the anti-skid. There was no speedo correction. This is my biggest irritation with GM over these trucks. As a comparision, Dodge can reflash it's trucks for 35" tall tires. GM need to get it together here.

Check out John Kennedy's website. http://www.kennedydiesel.com/

The Predator will correct the speedo reading and has some diagnostic features as well as some inctreased HP tunings. However, the tunings do not seem to be anywhere near as good as the Juice settings.

The Juice with Attitude has excellent performance tunings and provides EGT and Boost info. It will provide a corrected speedo reading, but only on the Attitude's monitor screen--not your speedo.

Superlift has a speed corretion unit that you splice into your wiring form the tranny to the speed sensor. Many of us are leery about this one because cutting into electical lines is a very easy way for a service dept to not honor your warranty.

None of these affect the transmission convertor's lock-up, as that input is based on the speed of the tranny output shaft. (JK told me this info.) This means that larger tires will delay your convertor lock up. Normally it is at 53 mph, with 285s it will lock up around 57 mph. This has not been an issue for me, amd my truck get's better mileage with the 285s than it did with the 265s.

Blaine

[TH]

Thanks Blaine....Taras

[TH]

afp...I've found a site that does this on the truck without need for add on boxes etc. Check out "westers_garage.eidnet.org/scprice.htm"

they can do any adjustments for any size tire that is computer related to your truck including speedometer, antilock braking, torque lock, transmission shifts etc. They also do horsepower, torque, fuel economy changes...

[afp]

The Predator does the same--computer reflash--thing and has a diagonostic function. However as long as our trucks are udr warranty I like the idea of being able to easily unplug it. Not to hide it from the dealer, but my dealership requires the truck be stock in such areas if it needs warranty service.

On top of that, the Juice is the class act of all power enhancements, and the Juice w/attitude gives you gauges as well. The Juice will not harm your tranny unless you deactivate all it's safety features. It's the only box right now that adds a no kiddin' 125 RWHP safely in a very useable rpm range.

Blaine

Blaine

[TH]

afp...you should go visit their site...you might be impressed...seems the US miltary is using their products...and I have a whole bunch of respect for the US Forces...so the product can't be that bad especially if the US miltary is outsourching to another country...Canada.

[afp]

I did go to their website. I am sure what they are offereing is fine, but when you're talking power enhancements, the Juice seems to provide the most useable power without harming the tranny. Fuel mileage is also good.

Please do as much research on power boxes as you have on suspension stuff before making your decision.

Blaine

[TH]

thanks afg...will do.